Nerve cuff for implantable electrode

ABSTRACT

A system for functional electrical stimulation can include a cuff and a stimulation device. The cuff can be attachable to a nerve or a muscle filament. The cuff can include an elastic collar configured to exert a force on the nerve or the muscle filament to reshape the nerve or the muscle filament to the internal configuration of an opening in the elastic collar. The stimulation device can be coupled to the cuff and configured to provide a stimulation waveform to the cuff.

This application claims the benefit of U.S. Provisional PatentApplication No. 60/822,403 filed 15 Aug. 2006, which is herebyincorporated in its entirety.

FIELD OF INVENTION

The invention relates to implantable biomedical devices and methods, andmore particularly to a cuff for selectively stimulating and/ormonitoring nerves or other biological soft tissue, and methods of usingsuch a cuff, including use as an electrode

BACKGROUND

Medical therapies have been developed that depend on the implantation ofdevices to selectively stimulate or monitor a patient's nerves or othersoft tissue. Functional electrical stimulation of the nervous system,for example, can be used to help to restore or maintain some degree oflost sensory and motor function in neurologically impaired individuals.In addition, there are certain specialized applications, such as thetreatment of sleep apnea, where it is necessary to simultaneouslymonitor and generate electrical signals in nerves. Implantableelectrical stimulation and/or recording devices include: (1) surfaceelectrodes placed on the skin surface to activate nerves in a generalregion of interest; (2) intra muscular and epimysial electrodes toactivate nerves to individual muscles; (3) the use of neural interfacesto address individual nerves; and (4) implantable cuff electrodes.

Cuff electrodes have been used for peripheral nerve stimulation and,among other advantages, generally require less energy to produce thedesired effects than either surface or intra muscular electrodes. Thesmaller power requirement may result in a potentially safer long termtherapy.

Half cuff electrodes generally have a C-shape cross-section, andcylindrical cuff electrodes can be spiral, helical, split-cylinder, orchambered cylinders. C-shape and split cylinder cuffs generally includea dielectric material defining a bore having sufficient diameter toreceive a nerve trunk to be electrically stimulated. One or morecontacts on the inner surface of the bore can be used to applyelectrical stimuli or monitor nerve activity. The electrical stimuli,for example, may be used to provide functional electrical stimulation,to block neural nerve impulses traveling along the nerve trunk, or tocause other effects.

The spiral type of cuff electrode typically includes a self-curlingsheet of non-conductive material biased-curl into a spiral. The spiralcuff also comes off the nerve very easily with a very small amount offorce, and can rotate around the nerve, making it difficult toconsistently identify and control the desired nerve fascicle. Conductivestrips or pads disposed on the self-curling sheet along a line extendingperipherally around the inner surface of the cuff. The conductivesegments may be electrically conductive for applying electrical impulsesor fluid conductive for infusing or extracting medications. In use, afirst edge of a self-curling sheet may be disposed adjacent a nervetruck around which the cuff is positioned. The self-curling sheet ispermitted to curl around the nerve forming an annular cuff.

The helix or helical cuff, similar to a telephone cord, acts as a springdue to its curved shape and allows a nerve to flex and permits morefluid exchange with surrounding tissue. This cuff must be wrapped aroundthe nerve, which is time consuming and difficult. The helix cuff can beopened and placed over the nerve and there is no closure mechanism, thehelix simply closes around the nerve when it is released. The helix cuffcan be removed from the nerve, however, very easily and sometimes doesnot provide the desired proximity to the nerve fascicle of interest.

U.S. Pat. No. 6,456,866 discloses another type of nerve cuff that isparticularly useful for functional electrical stimulation. The nervecuff described in that patent made it easier to precisely position thenerve cuff on a nerve and then to stimulate or monitor selected fibersof the nerves. One application both monitors and generates electricalsignals in the hypoglossal nerve for treatment of sleep apnea.

SUMMARY

The present invention provides an improved soft tissue cuff that issuitable for use as a nerve cuff electrode, for example. Theimprovements are related to one or more of: (i) closure of the electrodecuff, (ii) strain relief in the lead where it connects to the cuff,(iii) a slowly closing cuff, (iv) a recording electrode, and (v) anelectrode with an array of contacts that enable reversing therecruitment order of axons in a nerve bundle.

More particularly, the invention provides a biocompatible cuffcomprising a pair of members connected at a hinge end and securabletogether at a location removed from the hinge end via a closuremechanism that can secure the members in a closed condition.

The members can be made of silicon having a first hardness and theclosure mechanism includes at least one element made from a materialhaving a second hardness, which may be the same as or different from thefirst hardness. The closure mechanism can have a connector assembly withmale and female elements that snap together. The closure mechanism caninclude multiple spaced-apart connector assemblies. The members and theclosure mechanism can be molded as a single unit. The closure mechanismcan include self-aligning features. The closure mechanism can be securedusing a force applied along a common line of action.

The present invention also provides a method comprising the followingsteps: (a) placing a nerve cuff adjacent a nerve; and (b) closing thecuff around the nerve in a single step.

The invention also provides an electrode comprising a cuff and a leadextending from the cuff, where adjacent the cuff the lead passes througha resilient sleeve having a bent shape that reduces the transmission offorces from the lead to the cuff.

The bent shape can include a U-shape or an S-shape, for example, and thebent shape typically defines an angle of between 45 and 180 degrees.

The present invention also provides a system for functional electricalstimulation comprising a cuff for a nerve or muscle filament. The cuffincludes an elastic collar that exerts a force on the filament to causethe filament to gradually reshape to the internal configuration of anopening in the collar. The resulting pressure in the filament is lessthan 80 mmHG, and the elastic collar includes a biodegradeable materialthat dissolves in a body and thereby changes the pressure profile andreshapes the filament to the internal configuration of the opening inthe collar.

The present invention also provides a method for functional electricalstimulation comprising the following steps: (a) providing a stimulationapparatus, which, when operated, stimulates a nerve or muscle filament;(b) providing a monitoring apparatus, which, when operated, monitors abiological property of a nerve or muscle filament; (c) placing a cuffaround a nerve or muscle filament; and (d) applying a gradual force tothe nerve or muscle filament by means of the cuff which results in apressure in the nerve or muscle filament of less than 80 mmHg; operatingthe stimulation apparatus and; operating the monitoring apparatus.

The foregoing and other features of the invention are shown in thedrawings and particularly pointed out in the claims. The followingdescription and annexed drawings set forth in detail one or moreillustrative embodiments of the invention; this being indicative,however, of but one or a few of the various ways in which the principlesof the invention might be employed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic view of an exemplary system for functionalelectrical stimulation with a cuff applied to a nerve and a leadextending from the cuff to a control unit.

FIG. 1B is a schematic perspective view of a cuff.

FIG. 2 is a perspective view of a flat interface nerve electrode (FINE)provided by the present invention in an open condition.

FIG. 3 is a perspective view of the FINE of FIG. 2 in a closedcondition.

FIG. 4 is an enlarged partial side view of a portion of the FINE of FIG.3.

FIG. 5 is a perspective view of another embodiment of the FINE in aclosed condition.

FIG. 6 is a perspective view of the embodiment of FIG. 5 in an opencondition.

FIG. 7 is a schematic view of a cuff as initially placed around a nerveillustrating the forces applied to the nerve.

FIGS. 8A-8D are a sequence of schematic views of a slowly closingembodiment of the cuff provided by the present invention.

FIGS. 9A-9D are a sequence of images showing the process of the slowlyclosing embodiment closing over a period of time.

FIG. 10A is a perspective view of a model of a cat lateral gastrocnemius(LG) nerve and an electrode provided by the present invention.

FIG. 10B is a cross-sectional view of the electrode and LG nerve of FIG.10A.

DETAILED DESCRIPTION

The present invention provides one or more improvements to a cuff thatcan be used as part of an electrode, and particularly improves on theflat interface nerve electrode (FINE) disclosed in U.S. Pat. No.6,456,866, which is hereby incorporated by reference. Although the cuffis described primarily as providing electrical contacts for electricallystimulating or monitoring a nerve, the cuff may be adapted for use withother soft tissue, such as muscle. In addition or as an alternative tothe electrical capabilities of the cuff, the cuff can be adapted to actas a chemical dispenser or sensor. To simplify the description, the term“electrode” includes cuff designs for chemical dispensing or sensingthat lack electrical signal capabilities.

Referring now to the drawings, and particularly to FIGS. 1-4, theelectrode 10 includes a cuff 12 and a lead 14 extending from the cuff 12to a control unit 16. The cuff 12 includes a non-conductive band 18 withelectrical contacts 20 molded into the band. In use, the band 18encircles a nerve and gently and non-invasively applies a definedexterior force over time to redefine the geometry of the nerve, such asby flattening, thereby laterally spreading the fibers or fascicleswithin the nerve for selective stimulation or monitoring or both.

The driving force that urges the band inward is provided by mechanicalspring action at the active end of the cuff as well as the elasticnature of the cuff material. The illustrated design allows superficialplacement of the electrical contacts with selective access to the entireaxon population, with minimal damage to the nerve itself. The contactsare each capable of monitoring or activating separate and distinctregions within the nerve, along both the longitudinal and radial axis ofthe nerve, which generally was not previously accessible by other typesof electrode cuffs. The electrode also is capable of sensing smallneural signals with better signal to noise ratios due to the closeproximity of each of the contacts to separate axons comprising thefascicles.

The lower limit of applied pressure required to reshape the nerve issomething greater than that which is naturally occurring in an occurringnerve. This pressure is usually in the vicinity of 2 mmHG.

It is to be appreciated that by controlling the spring constant or forceexerted by the cuff surfaces, the cuff can be configured to rest againstthe surfaces of the epineurium membrane. The desired pressure, whichresults from the force applied by the cuff, is from about 2 to about 80mmHG; more preferably from about 3 to about 30 mmHG, and most preferablyfrom about 5 to about 15 mmHG.

The flat interface nerve electrode (FINE) shown applies small forces onopposing sides of the nerve while allowing room for the nerve to expandto the sides. In general, a small force does not significantly decreasenerve blood flow and will reshape the nerve into an elongated orflattened oval geometry that approximates the “ideal” geometry of a flatcable.

Each of the plurality of electrical contacts 20 are individuallyconnected to the lead 14 to the control unit 16, which can include anelectrical signal generating source or monitoring device. Fineconductive wires embedded in the band 18 extend from the contacts to alocation at an edge of the band to which the lead is attached. In thisway, the conductive wires are insulated from direct contact with eitherthe nerve, other conductors, or other surrounding tissue. Also, thenon-conductive band acts as a reinforcing structure and affords a levelof structural integrity to the somewhat otherwise frail conductors.

Although the illustrated embodiment shows the electrical contacts moldedinto the band, one alternative includes forming a micro-multi-contactarray in silicon using semiconductor fabrication technology. In thisway, active and intelligent electronics may be included on the cuffitself.

In use, the subject nerve is surgically accessed and the open side ofthe cuff is slipped over the nerve in the desired position. The cuff isopened as is shown in FIG. 2 and placed around the nerve. At this point,the distal ends of the band are brought together in a single step tosecure the cuff in place, completely encircling the nerve.

The FINE is shown as a pair of beams closed at the ends to form acontinuous band with a rectangular opening. The opening is not limitedto a rectangular shape, however. When the cuff is first placed around anerve, the beams are deformed around the nerve. The thickness (t), width(w), length (I), and cross-sectional profile of the beams, as well asthe properties of the selected material, will determine the magnitude ofthe force that will be applied to the nerve.

The following paragraphs describe improvements to the electrode,primarily to the structure of the cuff and the lead connected to thecuff. These improvements are related to (i) closure of the cuff, (ii)strain relief in the lead where it connects to the cuff, (iii) a slowlyclosing cuff, (iv) a recording electrode and (v) an electrode with anarray of contacts that enable reversing the recruitment order of axonsin a nerve bundle.

(i) Closure

The current FINE has a cuff with a pair of beam- or plate-like members22 connected together at a hinge side to form a pivoting clamp-likestructure. In previous embodiments of the FINE, the cuff was closed witha suture after the beam-like members had been placed around a nerve. Theresulting band surrounded the nerve and held the cuff in place relativeto the nerve. Given the size of the cuff, which can have a majordimension that is less than 20 mm, closing such a cuff with a suture canbe difficult to do during surgery.

The improvement provides a one step closure mechanism whereby the twoopposing beams are brought together and corresponding surfaces of thebeams are held together at a particular spacing in a single step. Inother words, the cuff is closed in a single motion, pushing the opposingbeams together, twisting the beams or otherwise moving the beams from anopen state to a closed state in a single motion without a change indirection.

An exemplary cuff is made primarily of silicone, and in particularsilicone with a range of hardness of about 30 to 90 Shore A, and moreparticularly about 40 to 70 Shore A. The closure mechanism can be formedof a silicone having a hardness that is different than the silicone usedin the cuff, but in an exemplary embodiment a substantial portion of thecuff is molded as a single unit. The closure mechanism is molded at thesame time as the cuff and includes male 24 and female 26 mating partsthat come together with a snap closure. The exemplary closure mechanismis self-aligning. Alternatively, the male parts can be added orotherwise formed in a subsequent step. The force required to disengagethe mating parts must be sufficient so that the closure mechanism willremain closed. If sufficient force is applied, however, the closuremechanism must open before it damages the nerve. An estimated force forclosing the closure mechanism is less than about 2 N (about 0.5 lbf.).The embodiment shown in FIGS. 2-4 has a closure mechanism with a singlemale-female-snap-connection connecting assembly. Longer or wider cuffscan have multiple connecting assemblies, as shown in FIG. 6, forexample.

The closure mechanism is not limited to the illustrated male and femalesnap closure elements. In addition to or as an alternative to thedescribed snap closure, the cuff may include an adhesive or cohesive, asliding or pivoting dovetail-type connection, or micro-hook-and-loopfasteners, for example.

Other types of cuff electrodes have required more effort to close. Onetype of cylinder cuff has a piano hinge closure mechanism on one sidewhere a pin (in the form of a flexible suture) is used to close thepiano hinge. This is a multi-step process, however. First the cylinderis closed, then a suture is threaded through the hinge parts and thenfinally tied off and trimmed. The cylinder-type cuff also would benefitfrom the closure mechanism described herein for the FINE cuff.

(ii) Strain Relief

In any electrical connection where a cable, such as for power or data,is connected to a device there is a mechanical weak point at theconnection point where failure is likely to occur.

In the case of an implantable electrode, it would be desirable tominimize the force applied to the cuff 12, and thus to the nerve, by thelead 14, as well as to minimize stress on the material where the leadattaches to the cuff. In this case, a bent shape 40, such as an S-shapeor a U-shape, is formed in the lead adjacent the cuff and a resilientsleeve 42 is molded in that shape so that the lead will retain its shapein the absence of any strain forces. When an axial (pulling) force isapplied to the lead, e.g., the bent shape straightens out until the benddisappears before significant force is transferred to the cuff. Thisprovides strain relief particularly in the longitudinal (along thegeneral axis of the lead), translational (side-to-side transverse to thelongitudinal direction) and even some torsional strain relief (twistingor rotating forces).

The surgeon implanting the electrode typically forms a loop, as shown at44, in the lead 14 during the surgical procedure, and this loop providesgross strain relief for larger forces applied to the lead. The bentsleeve 42 adjacent the cuff provides local relief on a smaller scale andreinforces the connection between the lead and the cuff. It also allowsthe lead to extend from the cuff, and thus from the nerve, at any anglewhile retaining substantially uniform flexibility in all directionstransverse the longitudinal direction.

This concept of providing strain relief is generally applicable to anytype of cuff, and is not limited to the FINE cuff.

(iii) Slowly Closing

The slowly closing cuff is intended to reduce the stress on a nerve thatis being flattened by having a cuff placed thereon. As shown in FIG. 7,at rest the cuff has a generally rectangular shape that is stretched outof shape when initially secured around the nerve. The cuff materialapplies a force F to the nerve as it returns to its original shape anddeforms the nerve.

The slowly closing cuff generally is designed with an opening heightlarger than the size of the nerve to accommodate initial swelling. Thecuff closes slowly to reshape the nerve into the desired flat geometry.The cuff is created by combining the reshaping properties of the FINEand the controllable degradation of Poly (DL lactic-co-glycolic) acid(PLGA). Bonding 50/50 or 65/35 PLGA to a stretched FINE can increase theopening heights (OH) on average from 0.1 mm to 1.66±0.45 and 2.05±0.55mm respectively. The addition of the PLGA films controls the time courseof closure over a period of 16±1 days and 14 to 16 hours for the 50/50and 65/35 slowly closing cuffs respectively.

In the slowly closing embodiment shown in FIGS. 8A-8D, a biodegradablematerial can be used to slowly change the forces exerted by the cuffover time as the material degrades in the patient's body. The regularcuff material provides a base. The base material is stretched and abiodegradable polymer is bonded onto the stretched base (FIG. 8B). Thisbi-layer cuff is then closed around the nerve in the usual fashion, andthe polymer degrades over time. As it degrades, the base material willwant to return to its original, typically flat, shape. Thus, the nerveis flattened slowly over time.

The flat interface nerve cuff slowly applies transverse pressure toopposing surfaces of the nerve, so as to spread the fascicles andflatten the epineurium membrane of the target nerve. This flatteningaction effectively allows the electrical contacts to interact withparticular fascicles through the epineurium membrane without puncturingeither the perineurium membrane, or the epineurium. Typically, the timeperiod required for the cuff to function properly extends from about one(1) hour to several days depending upon particular application andsituation.

This process is further illustrated in FIGS. 9A-9F. These time-lapseimages show the change in the shape of the opening defined by the cuffover a period of time, in this case twenty-eight days. As shown in FIG.9A, the opening in the cuff is substantially oval at the start. Overtime, as shown in FIGS. 9B-9F, the biodegradable polymer degrades untilthe opening in the cuff returns to a rectangular slit.

(iv) Recording

For recording-monitoring nerve signals, for example—a pair of referenceground points are provided on opposite sides of a recording electricalcontact along the length of the channel for receiving a nerve. Theembodiment shown in FIGS. 5 and 6 includes one recording contact 60 witha pair of reference grounds 62 and 64 equally spaced on opposing sidesof the recording contact. The equidistant spacing helps to reduce noiseand stimulation artifacts, thereby improving the electrode's sensitivityto a compound action potential in a target nerve. More than onerecording contact can be placed between the ground points. Thisrecording arrangement also can be used for stimulating the target nerve,but this design does not provide as much selectivity as thenon-recording embodiment. The recording electrode thus can providesimultaneous recording and selective stimulation of the desired nervefascicles.

(v) Reversing Recruitment Order

In this improvement to the FINE, an example of which is shown in FIGS.10A and 10B, a plurality of contacts are arrayed along the direction ofa cat lateral gastrocnemius (LG) nerve in multiple rows, with eachcontact aligned with the axons in the nerve and the spacing dependent oncharacteristics of the axons in the nerve. These contacts make itpossible to recruit smaller fascicles first before recruiting the largerfascicles. This is the opposite of the normal situation for the previousFINE. In other words, this allows for selectively recruiting axons orfascicles by diameter as well as selecting the desired fascicles thatproduce a desired effect. This concept requires additional multiplexingof the data signals, but may allow the electrode cuff to be used withmore complex nerves, such as the sciatic nerve, for example. Trial anderror can be used to determine which contacts produce a desired effect,such as control of the foot and ankle. Once the contacts that producethe desired effect are identified, those contacts can be permanentlyassigned to monitoring or stimulating their respective fascicles toachieve the desired results.

Although the invention has been shown and described with respect tocertain preferred embodiments, equivalent alterations and modificationswill occur to others skilled in the art upon reading and understandingthis specification and the annexed drawings. In particular regard to thevarious functions performed by the above described integers (components,assemblies, devices, compositions, etc.), the terms (including areference to a “means”) used to describe such integers are intended tocorrespond, unless otherwise indicated, to any integer which performsthe specified function of the described integer (i.e., that isfunctionally equivalent), even though not structurally equivalent to thedisclosed structure which performs the function in the hereinillustrated exemplary embodiment or embodiments of the invention. Inaddition, while a particular feature of the invention might have beendescribed above with respect to only one of several illustratedembodiments, such feature can be combined with one or more otherfeatures of the other embodiments, as can be desired and advantageousfor any given or particular application.

1-13. (canceled)
 14. A method for functional electrical stimulation,comprising the steps of: attaching a bi-layer cuff to a nerve or amuscle filament, wherein the bi-layer cuff comprises a base layerconfigured to return to an original shape and a biodegradable layerbonded onto the base layer; as the biodegradable layer degrades,applying a force to the nerve or the muscle as the base layer returns tothe original shape, wherein the force comprises a change to a pressureprofile; reshaping the nerve or the muscle filament based on the force;and closing the cuff around the nerve or the muscle filament.
 15. Themethod of claim 14, wherein the base layer comprises a pair of members,each comprising a silicon material.
 16. The method of claim 15, whereineach of the pair of members has an internal opening height larger thanthe diameter of the nerve or the muscle filament.
 17. The method ofclaim 14, wherein the reshaping further comprises reshaping the nerve orthe muscle filament to a new shape based on the original shape of thebase layer based on the force. Page 6
 18. The method of claim 17,wherein the new shape is flat.
 19. The method of claim 14, wherein thechange to the pressure profile is less than 80 mmHg.
 20. The method ofclaim 14, wherein the closing further comprises attaching the pair ofmembers together via a closure mechanism.
 21. The method of claim 20,wherein the closure mechanism is configured to self-align.
 22. Themethod of claim 20, wherein the base layer comprises a pair of memberspivotably connected at a hinge end; and the closure mechanism is opposedto the hinge end.
 23. The method of claim 20, wherein the closuremechanism comprises a connector assembly comprising a male element and afemale element configured to fit together to facilitate the closing. 24.The method of claim 14, wherein the reshaping is a gradual process basedon a degrading of a biodegradable material within the cuff.
 25. Themethod of claim 24, wherein the biodegradable material is abiodegradable polymer.
 26. The method of claim 14, further comprisingstimulating the nerve or the muscle filament via a current appliedthrough the closed cuff.